The present specification relates generally to trans-impedance amplifiers.
Trans-impedance amplifiers can be used to convert (or transform) an input current signal into an output voltage signal. A trans-impedance amplifier can be an active circuit with a transfer gain, or trans-impedance, of k=Vout/Iin (volts/amperes), where Iin is a magnitude of the input current signal and Vout is a magnitude of the output voltage signal. Ideally, a trans-impedance amplifier has a low input impedance (e.g., an input impedance equal to zero).
In practice, some applications of a trans-impedance amplifier can require that the trans-impedance amplifier be able to operate at multiple rates (e.g., 1 Gb/sec or 10 Gb/sec). A conventional multi-rate trans-impedance amplifier can switch between conversion at multiple rates by changing one or more impedances within the trans-impedance amplifier. Typically, switches in a signal path (e.g., switches in series with resistive elements in the trans-impedance amplifier) of the trans-impedance amplifier are used to change the impedances and switch between the multiple rates.
As an example, a conventional multi-rate trans-impedance amplifier can include a feedback subcircuit that includes a transistor in series with a first resistor. The series combination of the transistor and first resistor can be coupled in parallel to a second resistor. In the conventional multi-rate trans-impedance amplifier, switching from conversion at a first rate to a second rate can include enabling or disabling the transistor to change an equivalent impedance of the feedback subcircuit.